Observations of impurity transport in NSTX

Observations of impurity transport in NSTXObservations of impurity transport in NSTX

Luis F. Delgado-AparicioPrinceton Plasma Physics Laboratory

and the NSTX Research Team

4th ITPA Transport & Confinement MeetingCulham, Oxford, UK, 22-25 March 2010

NSTXNSTX Supported by

College W&MColorado Sch MinesColumbia UCompXGeneral AtomicsINELJohns Hopkins ULANLLLNLLodestarMITNova PhotonicsNew York UOld Dominion UORNLPPPLPSIPrinceton UPurdue USNLThink Tank, Inc.UC DavisUC IrvineUCLAUCSDU ColoradoU IllinoisU MarylandU RochesterU WashingtonU Wisconsin

Culham Sci CtrU St. Andrews

York UChubu UFukui U

Hiroshima UHyogo UKyoto U

Kyushu UKyushu Tokai U

NIFSNiigata UU Tokyo

JAEAHebrew UIoffe Inst

RRC Kurchatov InstTRINITI

KBSIKAIST

POSTECHASIPP

ENEA, FrascatiCEA, Cadarache

IPP, JülichIPP, Garching

ASCR, Czech RepU Quebec

NSTXNSTX 4th ITPA Transport & Confinement Meeting, Culham, Oxford, UK – Delgado-Aparicio March 22-25, 2010 2

In collaboration with…

D. Stutman, K. Tritz, M. Finkenthal and D. Kumar

Plasma Spectroscopy Group (PSG)

The Johns Hopkins University (JHU, USA)

R. Bell, S. Kaye, W. Solomon, B. LeBlanc,

J. Menard, S. Paul and C. H. Skinner

Princeton Plasma Physics Laboratory (PPPL)


Outline

1. Motivation and main diagnostic

1. Impurity transport experiments in NSTXa) * scan at fixed q-profileb) * scan of NBI heated H-modesc) First-cut results from momentum & particle

pinch experiment

3. Toroidal rotation effects on particle diffusivity

3. Future experiments, diagnostic needs & possible “areas” of collaborations


Motivation

Melted tungsten for the ITER-DT phase?

1. The understanding of impurity transport in magnetically confined fusion plasmas is one of the challenges facing the current fusion research.

2. Study the properties of impurity particle transport in a spherical tokakak (ST) in a variety of scenarios.

3. Important for extrapolation to the next step ST devices such as CTF and for comparison with the large aspect ratio tokamaks like ITER.


The main diagnostic for impurity transport used in NSTX is the tangential ME-SXR array

L. Delgado-Aparicio, et al.,

RSI, 75, 4020, (2004).

JAP, 102, 073304 (2007).

PPCF, 49, 1245 (2007).

NF, 49, 085028, (2009).

Magnetic axis(core)

NSTX top view


Outline



pinch experiment




Example 1: * scan at fixed q-profile

L. Delgado-Aparicio, et al., PPCF, 49, 1245 (2007).

L. Delgado-Aparicio, et al., NF, 49, 085028, (2009).

Ne puff Ne puff Ne puff

NSTXNSTX 4th ITPA Transport & Confinement Meeting, Culham, Oxford, UK – Delgado-Aparicio March 22-25, 2010

Experimental and simulated SXR profiles at low vs. high field

8

L. Delgado-Aparicio, et al., Nucl. Fusion, 49, 085028, (2009).


Experimental diffusivity in agreement with theoretical models

9


Note large increase in Dneo and Dexp at r/a>0.8


Convective velocity changes sign with BT

10


VZ<0 at r/a>0.5 at low-field is anomalous instabilities?⇒


Example 2: * scan of NBI heated H-modes

• * scan of NBI heated H-mode plasmas with n, Ip and B held constant.

• The high-power discharges have as much as twice the Ti,e in the gradient region (r/a~0.6-0.8).

• * vary up to a factor of four with nearly identical density profiles.

2 MW

4 MW

6 MW


Reconstructions show differences in SXR emissivities for low- & high- NBI power in the regions where * changed

12

1. The low-energy emissivities

(εLE-SXR~nNe8+, Ne9+) indicate that the core emissivity

decreases with NBI power while

increasing at the gradient region.

2. However, the high-energy emissivity

(εHE-SXR~nNe10+) indicate that both the core

and gradient region emissivity

increases with NBI power.


Charge state distribution can explain the differences in emissivity without the need of changing the transport

13

Preliminary results from MIST simulations indicate that a factor of two increases of Te (0.6<r/a<0.8) could be solely responsible for modifying the Ne charge state distribution and thus the SXR

emissivity, without the need of changing the underlying transport properties.


Outline



pinch experiment




Results from the momentum and particle transport experiments are on the way (w/W. Solomon and S. Kaye)

15

• The flattening effect during the n=3 braking seems to be stronger in the core than in the edge region.

• Get D & V from time-dependent MIST modeling.

• After the n=3 pulses the core impurity pile-up seem to be stronger; need to invoke inward Vpinch?


Outline



pinch experiment




Core impurity diffusivity can be affected by rotation in NSTX (×10-100 static DNeo)

C

O

Ar

Fe

Mo

Ne

Neon

DPS()

Neon-like Fe

DPS()Wong (‘87) & Romanelli (‘98)

Pfirsch-Schlüter Dneon()

MDV

Ti

1. Charge-states from

heavy impurities (Z≠A/2)

can have different DPS().

2. DPS() can be several

times larger than that of

the neoclassical transport

for stationary plasmas.

3.This is an additional

mechanism to explain

enhanced core

diffusivities without the

need of invoking the

presence of long

wavelength electrostatic

turbulence.

DPS(=0) DPS(=0)

a)b)

c)

d)


Pellet injection can probe enhanced core impurity transport

18

n C (

×10

12 c

m-3)

n C (

×10

12 c

m-3)

• Ablation resistant, vitreous C pellets deposits

impurity deep in the plasma.

• Evolution of nZ much slower than that of Te.

• DC around 1 m2/s for r/a > 0.6 (Neoclass. range).

• DC(r/a→core) > 1m2/s

NCLASSrange


Outline



pinch experiment




Density and impurity control is goal of multi-year Li program on NSTX

Lithium Research (LR) Topical Science Group:• XP-1002: Core impurity density and radiated power reduction using variations in LLD

divertor conditions (V. Soukhanovskii, LRNL).• XP-1024: Controlling Impurity Sources by Diffusive Lithium Injection (C. Skinner, PPPL).• XP-1027: RMPs below the ELM triggering threshold for impurity screening (J. Canik, ORNL).• XP-1056: Can Li Aerosol injection mitigate high-Z impurity accumulation during ELM-free

H-modes (D. Mansfield, PPPL)?

Advanced Scenario Topical Science Group:• XP-1005: Modifications to the early discharge evolution to reduce late impurity content

evolution (J. Menard, PPPL).• XP-1006: Development of High-Elongation Beam Heated Scenarios with Reduced Impurity

Content and Increased Non-Inductive Fraction (S. Gerhart, PPPL).• XP-1007: Use of HHFW heating to increase the non-inductive current fraction in NBI

produced H-mode plasmas with triggered ELMs to control impurity buildup (M.

Bell, PPPL).


New ME-SXR diagnostics will enable transport experiments probing also Z-dependence

• Increased spatial resolution (~1 cm) probing the edge and gradient region.

• Five broadband energy ranges will allow estimates of C, O, Ne, Ar and Fe transport.

(Courtesy of K. Tritz - JHU)


Possibility of joint experiments(…just some ideas for 2011)

1. Study relationship between D & V and rotation (important for NSTX, NHTX and CTF).

• Use NBI and/or n=3 magnetic braking.• Use different impurities.• Exp. tests vs. Wong/Romanelli’s

model.

2. Relationship between Vp and central electron heating in NSTX.

• Use HHFW heating →Te/Ti~1-4.

• Compare with NBI→Te/Ti~1

• Z-scaling of impurity transport.• C, O, Ne, Ar and metals!• Reviving the pellet injector.

4. Study relationship between resonant magnetic perturbations and edge transport.

• 3D-non-axisymmetric perturbations.• MHD events such as RWMs & ELMs.• Magnetic ELM-pace experiments.

i. Impurity transport.

ii. “Flushing” impurities from core.

5. Measuring He transport in NSTX.• Right diagnostic not working yet!• Good time/spatial resolution.

(5-10 ms, 1-4 cm)• Diagnostic based on beam emission.

i. SXR trans. grating spectro. (JHU).

ii. Scanning visible spectro. (PPPL).


Acknowledgements

23

• The Johns Hopkins University: Gaib Morris, Scott Spangler, Steve Patterson, Russ Pelton and Joe Ondorff.

• Princeton Plasma Physics Laboratory: Bill Blanchard, Patti Bruno, Thomas Czeizinger, John Desandro, Russ Feder, Jerry Gething, Scott Gifford, Bob Hitchner, James Kukon, Doug Labrie, Steve Langish, Jim Taylor, Sylvester Vinson, Doug Voorhes and Joe Winston (NSTX).

• This work was supported by U.S. DoE Contract No. DE-AC02-09CH11466 at PPPL and DoE grant No. DE-FG02-99ER5452 at Johns Hopkins University.


EXTRAS


Add an extrinsic impurity for transport studies


Ne gas-puff technique proven useful in MHD experiments

26

1. The earlier appearance of the NTM appear to be due to the enhanced Prad.

1. Verifying the linear-dependence of the island-width growth-rate with ∙Prad is

important, as it predicts that tokamaks can be susceptible to TM destabilization by

impurity radiation.

Study of radiation induced tearing modes

Studying the correlations between magnetic and kinetic diagnostics

for resistive wall mode identification


Rotation can increase the stationary DPfirsch-Slüter

• K. L. Wong, et al., PRL, 59, 2643, (1987); Phys. Fluids B 1, 545, (1989).

• M. Romanelli, et al., Plasma Phys. Control. Fusion, 40, 1767, (1998).

• Although Wong and Romanelli’s results were derived using different

methods, the neoclassical enhancement due to rotation is the SAME!

∴ Neoclassical diffusivity for heavy impurities can be one to two orders of magnitude higher in a rotating plasma than in a stationary one without the need of invoking the presence of long wavelength electrostatic turbulence.


Core impurity diffusivity can be affected by rotation in NSTX (×10-100 static DNeo)

C

O

Ar

Fe

Mo

Ne

Neon

DPS()

Neon-like Fe

DPS()Wong (‘87) & Romanelli (‘98)

Pfirsch-Schlüter Dneon()

MDV

Ti

Can be tested using:

a)Pellet injection

b)Laser blow-off

c)Balanced NBI

d)n=3 mag. braking

e)Argon injection

DPS(=0) DPS(=0)

a)

c)

d)

b)

Observations of impurity transport in NSTX

Documents

Transcript of Observations of impurity transport in NSTX